Oh it's bigger and more powerful than a Corolla alright. It's a whole size car larger, more like Camry/Accord size, pretty much a ringer for a Hyundai Sonata (which makes sense, given that Hyundai owns Kia). But because it's a cheapo brand compared to the Corolla they both get to live in C class, or at least for now they do I guess. I'd rather have the Optima, wasn't too bad when I drove recently, but for me it was still just a marginally comfortable seating position (Optima/Sonata) vs really uncomfortable seating position (Corolla).

If you have your receipt (or look it up online) you can confirm what class they say the Optima was for your rental. It usually says what class you took out even if it was an upgrade from what you booked. (Also says on the key tag, of course, but a bit too late for that. )

Neverlost for free is certainly an upgrade of sorts, although if you didn't book it it's probably just a toy to play with vs actually needing it.